The Role of MEF2 Transcription Factor Family in Neuronal Survival and Degeneration

The family of myocyte enhancer factor 2 (MEF2) transcription factors comprises four highly conserved members that play an important role in the nervous system. They appear in precisely defined time frames in the developing brain to turn on and turn off genes affecting growth, pruning and survival of neurons. MEF2s are known to dictate neuronal development, synaptic plasticity and restrict the number of synapses in the hippocampus, thus affecting learning and memory formation. In primary neurons, negative regulation of MEF2 activity by external stimuli or stress conditions is known to induce apoptosis, albeit the pro or antiapoptotic action of MEF2 depends on the neuronal maturation stage. By contrast, enhancement of MEF2 transcriptional activity protects neurons from apoptotic death both in vitro and in preclinical models of neurodegenerative diseases. A growing body of evidence places this transcription factor in the center of many neuropathologies associated with age-dependent neuronal dysfunctions or gradual but irreversible neuron loss. In this work, we discuss how the altered function of MEF2s during development and in adulthood affecting neuronal survival may be linked to neuropsychiatric disorders.

Decorin Induces Cardiac Hypertrophy by Regulating the CaMKII/MEF-2 Signaling Pathway In Vivo

OBJECTIVE

Cardiac hypertrophy is an adaptive reaction of the heart against cardiac overloading, but continuous cardiac hypertrophy can lead to cardiac remodeling and heart failure. Cardiac hypertrophy is mostly considered reversible, and recent studies have indicated that decorin not only prevents cardiac fibrosis associated with hypertension, but also achieves therapeutic effects by blocking fibrosis-related signaling pathways. However, the mechanism of action of decorin remains unknown and unconfirmed.

METHODS

We determined the degree of myocardial hypertrophy by measuring the ratios of the heart weight/body weight and left ventricular weight/body weight, histological analysis and immunohistochemistry. Western blotting was performed to detect the expression levels of CaMKII, p-CaMKII and MEF-2 in the heart.

RESULTS

Our results confirmed that decorin can regulate the CaMKII/MEF-2 signaling pathway, with inhibition thereof being similar to that of decorin in reducing cardiac hypertrophy.

CONCLUSION

Taken together, the results of the present study showed that decorin induced cardiac hypertrophy by regulating the CaMKII/MEF-2 signaling pathway in vivo, revealing a new therapeutic approach for the prevention of cardiac hypertrophy.

Inflammation leads through PGE/EP3 signaling to HDAC5/MEF2-dependent transcription in cardiac myocytes

The myocyte enhancer factor 2 (MEF2) regulates transcription in cardiac myocytes and adverse remodeling of adult hearts. Activators of G protein-coupled receptors (GPCRs) have been reported to activate MEF2, but a comprehensive analysis of GPCR activators that regulate MEF2 has to our knowledge not been performed. Here, we tested several GPCR agonists regarding their ability to activate a MEF2 reporter in neonatal rat ventricular myocytes. The inflammatory mediator prostaglandin E₂ (PGE₂) strongly activated MEF2. Using pharmacological and protein-based inhibitors, we demonstrated that PGE₂ regulates MEF2 via the EP₃ receptor, the βγ subunit of G_i/o protein and two concomitantly activated downstream pathways. The first consists of Tiam1, Rac1, and its effector p21-activated kinase 2, the second of protein kinase D. Both pathways converge on and inactivate histone deacetylase 5 (HDAC5) and thereby de-repress MEF2. In vivo, endotoxemia in MEF2-reporter mice induced upregulation of PGE₂ and MEF2 activation. Our findings provide an unexpected new link between inflammation and cardiac remodeling by de-repression of MEF2 through HDAC5 inactivation, which has potential implications for new strategies to treat inflammatory cardiomyopathies.

Salvianolic Acid B Inhibits Activation of Human Primary Hepatic Stellate Cells Through Downregulation of the Myocyte Enhancer Factor 2 Signaling Pathway

Various isoforms of myocyte enhancer factor 2 (MEF2) have been shown to play a role in the activation of rat hepatic stellate cells (HSCs) in culture. The signals that regulate MEF2 in HSCs are unknown. In addition, whether MEF2s regulate the activation of human HSCs (H-HSCs) is unclear. Here, we studied the expression and function of MEF2s in H-HSCs. Our data showed that the levels of MEF2A, C, and D proteins were high in liver tissues from patients with cirrhosis and increased during culture-induced activation of primary H-HSCs. Exposure of H-HSCs to transforming growth factor beta 1 (TGF-β1) led to a significant increase in MEF2A and C protein levels and enhanced MEF2 activity. Interestingly, TGF-β1 did not further enhance MEF2D levels. Furthermore, TGF-β1 activated p38 mitogen-activated protein kinase (MAPK) and led to increased phosphorylation of MEF2C at its p38 recognition site. Inhibition of p38 MAPK inhibited both TGF-β1- and culture-induced activation of MEF2. The activity of collagen I reporter in H-HSCs was significantly reduced when MEF2A and MEF2C were blocked with overexpression of dominant negative MEF2 mutants. Salvianolic-acid B (SA-B), a water-soluble element of Salvia miltiorrhiza known to have anti-fibrosis effects, attenuated both basal and TGF-β1-induced increased levels of MEF2A and C mRNA and protein. In addition, SA-B inhibited MEF2 activity, which correlated with reduced expression of the HSC activation markers, α-smooth muscle actin (α-SMA), and collagen I. Administration of SA-B reduced MEF2A in vivo, which was accompanied by reduced levels of α-SMA in a model of dimethylnitrosamine-induced rat liver fibrosis. We concluded that the MEF2 transcription factor was stimulated by TGF-β1 in H-HSCs. Antagonizing TGF-β1-induced activation of the MEF2 signaling pathway may account in part for the anti-fibrosis effects of SA-B.

CAPE increases the expression of SOD3 through epigenetics in human retinal endothelial cells

Extracellular-superoxide dismutase (EC-SOD or SOD3), which catalyzes the dismutation of superoxide anions into hydrogen peroxide, plays a key role in vascular protection against reactive oxygen species (ROS). The excess generation of ROS is closely involved in the pathogenesis of diabetic retinopathy (DR); therefore, the maintenance of SOD3 expression at high levels is important for the prevention of DR. In the present study, we showed that caffeic acid phenethyl ester (CAPE) increased the expression of SOD3 through the acetylation of histone within the SOD3 promoter region in human retinal endothelial cells (HRECs). Histone acetylation within its promoter was focused on the inhibition of histone deacetylase (HDAC), and we examined the involvement of myocyte enhancer factor 2 (MEF2) and HDAC1 in CAPE-elicited SOD3 expression. Our results demonstrate that SOD3 silencing in basal HRECs is regulated by HDAC1 composed with MEF2A/2D hetero dimers. Moreover, phosphorylation of threonine 312 in MEF2A and dissociation of HDAC1 from SOD3 promoter play pivotal roles in CAPE-elicited SOD3 expression. Overall, our findings provide that CAPE may be one of the seed compounds that maintain redox homeostasis.

A traditional Chinese medicine, Lujiao prescription, as a potential therapy for hypertrophic cardiomyocytes by acting on histone acetylation

BACKGROUND

Chronic heart failure (CHF) is a complex clinical syndrome, and a serious stage of various heart diseases. Dysfunction of histone acetylation is involved in pathogenesis of CHF. Lujiao is a clinical and traditional prescription that has been previously used in the treatment of heart failure. The objective of our study was to explore the effects of traditional Chinese Medicine intervention with Lujiao prescription on hypertrophic cardiomyocytes with histone acetylation abnormality.

METHODS

Myocardial cells from neonatal rats were stimulated via phenylephrine (PE) and then randomly divided into seven groups: normal group (without any treatment), model group (treated with saline), TSA group (treated with trichostatin A), perindopril group (treated with perindopril), and the high, medium, and low dose of Lujiao groups (treated with 2.4 g/mL, 1.2 g/mL, and 0.6 g/mL of Lujiao, respectively). The test drug of perindopril group or Lujiao group was derived from serum after drug treatment in rats. Real-time polymerase chain reaction and Western blot were performed to analyze expression of myocyte enhancer factor 2 (MEF-2), α-major histocompatibility complex (MHC), and β-MHC and acetylation level of histone H3.

RESULTS

Expressions of MEF-2 and β-MHC were significantly increased after PE treatment and decreased after drug treatment. Expression of α-MHC mRNA was significantly reduced after PE treatment and increased after being treated with Lujiao prescription, perindopril, and TSA. The acetylation level of histone H3 decreased in rat myocardial cells stimulated by PE 48 for hours and this decrease was reversed after treatment with high and medium doses of Lujiao prescription, perindopril and TSA.

CONCLUSION

Histone acetylation-MEF-2-α-MHC/β-MHC axis was discovered in myocardial hypertrophy, and intervention of Lujiao prescription exhibited good effects.

Novel Targets for the Transcription Factors MEF2 in MA-10 Leydig Cells

Testosterone production by Leydig cells is a tightly regulated process requiring synchronized expression of several steroidogenic genes by numerous transcription factors. Myocyte enhancer factor 2 (MEF2) are transcription factors recently identified in somatic cells of the male gonad. In other tissues, MEF2 factors are essential regulators of organogenesis and cell differentiation. So far in the testis, MEF2 factors were found to regulate Leydig cell steroidogenesis by controlling Nr4a1 and Star gene expression. To expand our understanding of the role of MEF2 in Leydig cells, we performed microarray analyses of MEF2-depleted MA-10 Leydig cells, and the results were analyzed using Partek and Ingenuity Pathway Analysis software. Several genes were differentially expressed in MEF2-depleted Leydig cells, and 16 were validated by quantitative RT-PCR. A large number of these genes are known to be involved in fertility, gonad morphology, and steroidogenesis. These include Ahr, Bmal1, Cyp1b1, Hsd3b1, Hsd17b7, Map2k1, Nr0b2, Pde8a, Por, Smad4, Star, and Tsc22d3, which were all downregulated in the absence of MEF2. In silico analyses revealed the presence of MEF2-binding sites within the first 2 kb upstream of the transcription start site of the Por, Bmal1, and Nr0b2 promoters, suggesting direct regulation by MEF2. Using transient transfections in MA-10 Leydig cells, small interfering RNA knockdown, and a MEF2-Engrailed dominant negative, we found that MEF2 activates the Por, Bmal1, and Nr0b2 promoters and that this requires an intact MEF2 element. Our results identify novel target genes for MEF2 and define MEF2 as an important regulator of Leydig cell function and male reproduction.

Regulation of energy metabolism by long-chain fatty acids

In mammals, excess energy is stored primarily as triglycerides, which are mobilized when energy demands arise. This review mainly focuses on the role of long chain fatty acids (LCFAs) in regulating energy metabolism as ligands of peroxisome proliferator-activated receptors (PPARs). PPAR-alpha expressed primarily in liver is essential for metabolic adaptation to starvation by inducing genes for beta-oxidation and ketogenesis and by downregulating energy expenditure through fibroblast growth factor 21. PPAR-delta is highly expressed in skeletal muscle and induces genes for LCFA oxidation during fasting and endurance exercise. PPAR-delta also regulates glucose metabolism and mitochondrial biogenesis by inducing FOXO1 and PGC1-alpha. Genes targeted by PPAR-gamma in adipocytes suggest that PPAR-gamma senses incoming non-esterified LCFAs and induces the pathways to store LCFAs as triglycerides. Adiponectin, another important target of PPAR-gamma may act as a spacer between adipocytes to maintain their metabolic activity and insulin sensitivity. Another topic of this review is effects of skin LCFAs on energy metabolism. Specific LCFAs are required for the synthesis of skin lipids, which are essential for water barrier and thermal insulation functions of the skin. Disturbance of skin lipid metabolism often causes apparent resistance to developing obesity at the expense of normal skin function.

Regulation of Akt-mTOR, ubiquitin-proteasome and autophagy-lysosome pathways in response to formoterol administration in rat skeletal muscle

Administration of β2-agonists triggers skeletal muscle anabolism and hypertrophy. We investigated the time course of the molecular events responsible for rat skeletal muscle hypertrophy in response to 1, 3 and 10 days of formoterol administration (i.p. 2000μg/kg/day). A marked hypertrophy of rat tibialis anterior muscle culminated at day 10. Phosphorylation of Akt, ribosomal protein S6, 4E-BP1 and ERK1/2 was increased at day 3, but returned to control level at day 10. This could lead to a transient increase in protein translation and could explain previous studies that reported increase in protein synthesis following β2-agonist administration. Formoterol administration was also associated with a significant reduction in MAFbx/atrogin-1 mRNA level (day 3), suggesting that formoterol can also affect protein degradation of MAFbx/atrogin1 targeted substrates, including MyoD and eukaryotic initiation factor-3f (eIF3-f). Surprisingly, mRNA level of autophagy-related genes, light chain 3 beta (LC3b) and gamma-aminobutyric acid receptor-associated protein-like 1 (Gabarapl1), as well as lysosomal hydrolases, cathepsin B and cathepsin L, was significantly and transiently increased after 1 and/or 3 days, suggesting that autophagosome formation would be increased in response to formoterol administration. However, this has to be relativized since the mRNA level of Unc-51-like kinase1 (Ulk1), BCL2/adenovirus E1B interacting protein3 (Bnip3), and transcription factor EB (TFEB), as well as the protein content of Ulk1, Atg13, Atg5-Atg12 complex and p62/Sqstm1 remained unchanged or was even decreased in response to formoterol administration. These results demonstrate that the effects of formoterol are mediated, in part, through the activation of Akt-mTOR pathway and that other signaling pathways become more important in the regulation of skeletal muscle mass with chronic administration of β2-agonists.

Differential striatal spine pathology in Parkinson's disease and cocaine addiction: a key role of dopamine?

In the striatum, the dendritic tree of the two main populations of projection neurons, called "medium spiny neurons (MSNs)", are covered with spines that receive glutamatergic inputs from the cerebral cortex and thalamus. In Parkinson's disease (PD), striatal MSNs undergo an important loss of dendritic spines, whereas aberrant overgrowth of striatal spines occurs following chronic cocaine exposure. This review examines the possibility that opposite dopamine dysregulation is one of the key factors that underlies these structural changes. In PD, nigrostriatal dopamine degeneration results in a significant loss of dendritic spines in the dorsal striatum, while rodents chronically exposed to cocaine and other psychostimulants, display an increase in the density of "thin and immature" spines in the nucleus accumbens (NAc). In rodent models of PD, there is evidence that D2 dopamine receptor-containing MSNs are preferentially affected, while D1-positive cells are the main targets of increased spine density in models of addiction. However, such specificity remains to be established in primates. Although the link between the extent of striatal spine changes and the behavioral deficits associated with these disorders remains controversial, there is unequivocal evidence that glutamatergic synaptic transmission is significantly altered in both diseased conditions. Recent studies have suggested that opposite calcium-mediated regulation of the transcription factor myocyte enhancer factor 2 (MEF2) function induces these structural defects. In conclusion, there is strong evidence that dopamine is a major, but not the sole, regulator of striatal spine pathology in PD and addiction to psychostimulants. Further studies of the role of glutamate and other genes associated with spine plasticity in mediating these effects are warranted.

Hippocampal CA1 region shows differential regulation of gene expression in mice displaying extremes in behavioral sensitization to amphetamine: relevance for psychosis susceptibility?

RATIONALE

Psychosis susceptibility is mediated in part by the dopaminergic neurotransmitter system. In humans, individual differences in vulnerability for psychosis are reflected in differential sensitivity for psychostimulants such as amphetamine. We hypothesize that the same genes and pathways underlying behavioral sensitization in mice are also involved in the vulnerability to psychosis.

OBJECTIVES

The aim of the current study was to investigate which genes and pathways may contribute to behavioral sensitization in different dopaminergic output areas in the mouse brain.

METHODS

We took advantage of the naturally occurring difference in psychostimulant sensitivity in DBA/2 mice and selected animals displaying extremes in behavioral sensitization to amphetamine. Subsequently, the dopamine output areas, prefrontal cortex, nucleus accumbens, and cornu ammonis 1 (CA1) area of the hippocampus, were isolated by laser microdissection and subjected to DNA microarray analysis 1 h after a challenge dose of amphetamine.

RESULTS

A large number of genes with differential expression between high and low responders were identified, with no overlap between brain regions. Validation of these gene expression changes with real-time quantitative polymerase chain reaction demonstrated that the most robust and reproducible effects on gene expression were in the CA1 region of the hippocampus. Interestingly, many of the validated genes in CA1 are members of the cAMP response element (CRE) family and targets of the glucocorticoid receptor (GR) and myocyte enhancer factor 2 (Mef2) transcription factors.

CONCLUSION

We hypothesize that CRE, Mef2, and GR signaling form a transcription regulating network, which underlies differential amphetamine sensitivity, and therefore, may play an important role in susceptibility to psychosis.